Fischer: Know your valve’s limitations 

Robert L. Fischer, P.E., is a physicist and electrical engineer who spent 25 years in chemical crops and refineries. Fischer can also be a part-time college professor. He is the principal reliability advisor for Fischer Technical Services. He could also be reached at
One of Dirty Harry’s well-known quotes was: “A man’s received to know his limitations.” This story illustrates why you have to know your management valve’s limitations.
A client recently called for assist downsizing burners on a thermal oxidizer. Changes within the manufacturing process had resulted in an excessive amount of heat from the present burners. All attempts to lower temperatures had led to unstable flames, flameouts and shutdowns. The greater temperatures didn’t hurt the product however the burners have been guzzling a hundred and ten gallons of propane each hour. Given the excessive cost of propane at that plant, there were, literally, tens of millions of incentives to conserve power and cut back prices.
Figure 1. Operation of a cross related air/gas ratio regulator supplying a nozzle mix burner system. The North American Combustion Practical Pointers book may be found on-line at Fives North American Combustion, Inc. 4455 East 71st Street, Cleveland, OH 44015. Image courtesy of Fives North American Combustion, Inc.
A capital project to retrofit smaller burners was being written. One of the plant’s engineers known as for a worth estimate to change burner controls. As we mentioned their efforts to scale back fuel usage, we realized smaller burners may not be required to resolve the issue.
Oxidizer temperature is principally determined by the position of a “combustion air” control valve. Figure 1 shows how opening that valve will increase stress in the combustion air piping. Higher pressure forces extra air via the burners. An “impulse line” transmits the air stress to 1 aspect of a diaphragm within the “gas control valve” actuator. As air strain on the diaphragm increases, the diaphragm moves to open the valve.
The gas valve is automatically “slaved” to the combustion air being equipped to the burner. Diaphragm spring pressure is adjusted to ship the 10-to-1 air-to-gas ratio required for secure flame.
The plant was unable to maintain flame stability at considerably lower gas flows as a outcome of there’s a restricted range over which any given diaphragm spring actuator can provide accurate control of valve place. This usable control vary is known as the “turndown ratio” of the valve.
In this case, the plant operators no longer wanted to fully open the gasoline valve. They needed finer decision of valve position with a lot lower combustion air flows. The diaphragm actuator wanted to find a way to crack open after which management the valve using considerably lower pressures being delivered by the impulse line. Fortunately, changing เกจวัดความดันpressuregauge was all that was required to permit recalibration of the gasoline valve actuator — utilizing the prevailing burners.
Dirty Harry would undoubtedly approve of this cost-effective change to the valve’s low-flow “limitations.” No capital project. No burner replacements. No vital downtime. Only a few cheap elements and minor rewiring were required to keep away from wasting “a fistful of dollars.”

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